Image generating apparatus and method therefor

ABSTRACT

An apparatus comprises a determiner ( 305 ) which determines a first-eye and a second eye view pose. A receiver ( 301 ) receives a reference first-eye image with associated depth values and a reference second-eye image with associated depth values, the reference first-eye image being for a first-eye reference pose and the reference second-eye image being for a second-eye reference pose. A depth processor ( 311 ) determines a reference depth value, and modifiers ( 307 ) generate modified depth values by reducing a difference between the received depth values and the reference depth value by an amount that depends on a difference between the second or first-eye view pose and the second or first-eye reference pose. A synthesizer ( 303 ) synthesizes an output first-eye image for the first-eye view pose by view shifting the reference first-eye image and an output second-eye image for the second-eye view pose by view shifting the reference second-eye image based on the modified depth values. The terms first and second may be replaced by left and right, respectively or vice verse. E.g. the terms first-eye view pose, second-eye view pose, reference first-eye image, and reference second-eye image may be replaced by left-eye view pose, right-eye view pose, reference left-eye image, and reference right-eye image, respectively.

FIELD OF THE INVENTION

The invention relates to image generation from first-eye and second-eyeimages and associated depth, and in particular, but not exclusively, toimage generation for e.g. limited virtual reality applications andservices.

BACKGROUND OF THE INVENTION

The variety and range of image and video applications have increasedsubstantially in recent years with new services and ways of utilizingand consuming video being continuously developed and introduced.

For example, one service being increasingly popular is the provision ofimage sequences in such a way that the viewer is able to actively anddynamically interact with the system to change parameters of therendering. A very appealing feature in many applications is the abilityto change the effective viewing position and viewing direction (theviewing pose) of the viewer, such as for example allowing the viewer tomove and “look around” in the scene being presented. Such a feature canspecifically enable a virtual reality experience being provided to auser.

It is also desirable for many applications, that the image beingpresented is a three-dimensional image. Indeed, in order to optimizeimmersion of the viewer, it is typically preferred for the user toexperience the presented scene as a three-dimensional scene.

A major issue in supporting various services based on, in particularthree dimensional, representations of a scene is that a large amount ofdata is required. This results in high resource requirements, such as aneed for large storage resources. However, in many scenarios, thebiggest constraint is not storage or processing requirements butcommunication requirements. If it is required that the data representingthe scene must be communicated over a bandwidth limited communicationchannel (whether internal or external), it is highly desirable to try toreduce the amount of data that needs to be communicated.

For example, in many scenarios and for many applications, a clientserver approach may be used wherein a remote client executing e.g. avirtual reality application is coupled to a central service thatprovides the required scene data over a bandwidth limited link.

A particular proposed service seeks to provide a limited virtual realityexperience by allowing a 3D experience that adapts to the user'smovements as long as these are small and do not differentiate too farfrom a given reference point. For example, a 3D experience of a scenemay be provided for a given virtual viewpoint with the experienceadapting to the user making small head movements while essentiallystaying in the same spot. For example, the service may provide anexperience where the rendered 3D view follows movements such as noddingor shaking the head but does not follow if the user moves his headsubstantially to the side. A service may provide a full 3D experience aslong as the user's eyes remain within a small sweet spot. This sweetspot may for each eye have an extent of only a few centimeters.

Such an approach may allow a high quality 3D experience to be providedbased on a limited amount of data, both in terms of captured andcommunicated data. Typically, a-left-eye image and a-right eye imagewith associated depth maps may be provided to a local renderer. Therenderer may then generate view images for the current view based on thereceived images and the depth maps for positions that are very close to(within the sweet spot area of) the nominal position. This may provide avery natural experience in many scenarios while maintaining a very lowdata rate. For example, for a conference application, the provision of atwo image streams (one for each eye) and associated depth data may allowa 3D representation of the remote end with consistent stereopsis andmotion parallax as long as the user remains in the same position andonly makes small head movements. Thus, a very natural and high qualityexperience can be provided.

However, an issue with such services is that the user may potentiallymove outside the sweet spot. This will tend to result in a fast andsignificant degradation in image quality, including the introduction ofperceptible artefacts (e.g. due to a lack of de-occlusion data). In manycases, the quality may degrade very quickly resulting in a veryundesirable user experience.

Different solutions have been proposed to this problem. Many systems arearranged to increasingly blur or darken the image as the user moves awayfrom the preferred position and sweet spot. In many cases, when the usermoves outside the sweet spot, the viewer is presented a blurred pictureor a black picture. This of course hides the quality degradation andalso tends to bias the user towards remaining in the sweet spot.

However, current solutions tend not to be optimal in terms of userexperience, data rate, complexity etc.

Hence, an improved approach for synthesizing images would beadvantageous. In particular, an approach that allows improved operation,facilitated operation, improved quality, increased flexibility,facilitated implementation, facilitated operation, reduced data rate,reduced data storage, distribution, and/or processing resourcerequirements, improved adaptability, improved image quality, improveduser experience, and/or improved performance would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, the Invention seeks to preferably mitigate, alleviate oreliminate one or more of the above mentioned disadvantages singly or inany combination.

According to an aspect of the invention there is provided an imagegenerating apparatus comprising: a determiner for determining afirst-eye view pose and a second-eye view pose; a receiver for receivinga reference first-eye image with associated first depth values and areference second-eye image with associated second depth values, thereference first-eye image being for a first-eye reference pose and thereference second-eye image being for a second-eye reference pose; adepth processor for determining a reference depth value; a firstmodifier for generating modified first depth values by reducing adifference between the first depth values and the reference depth valueby a first amount dependent on a difference between the first-eye viewpose and the first-eye reference pose; a second modifier for generatingmodified second depth values by reducing a difference between the seconddepth values and the reference depth value by a second amount dependenton a difference between the second-eye view pose and the second-eyereference pose; and a synthesizer for synthesizing an output first-eyeimage for the first-eye view pose by view shifting the referencefirst-eye image based on the modified first depth values and an outputsecond-eye image for the second-eye view pose by view shifting thereference second-eye image based on the modified second depth values.

The invention may allow an improved user experience in many embodimentsand scenarios. The approach may in many scenarios allow an increasedfreedom of movement of a viewer and may reduce the perceived degradationwhen a viewer moves outside the sweet spot. The approach may allow animproved trade-off between image quality degradation from view shiftingand spatial distortion. In many scenarios, the approach may allow animproved gradual deterioration of perceived image quality withincreasing distance from a view pose to a reference view pose for whichimage data is provided. The approach may further allow advantageousoperation while having a low complexity and/or resource usage and/or mayallow facilitated implementation.

The approach may for example allow three dimensional perception of ascene even for view poses or positions that differ by an amount whereview shifting may tend to be unreliable or introduce substantialartefacts.

A pose may be a position and/or orientation. A difference between posesmay for example be a Euclidian distance between the correspondingpositions and/or may e.g. be an angular distance between correspondingorientations (or of course a combined measure of both Euclidian andangular distance).

The difference between the view pose and the reference pose for thefirst eye and/or second eye may be determined in accordance with anysuitable distance or difference measure. The difference may for examplebe determined as a monotonically increasing function of a distancebetween a position of the view pose and a position of the reference poseand/or a monotonically increasing function of an (absolute value of an)angular difference between an orientation of the view pose and anorientation of the reference pose.

The view pose may for example be determined relative to the referenceposes. For example, at a given time instant, the current view pose maybe designated to correspond to the reference view pose. Thus, for thatview pose no view shifting is necessary to generate the output images,or equivalently the received images may be set to represent view imagesfor that view pose. Subsequent view poses may then be determinedrelative to the view pose designated to correspond to the referencepose. Such a process of linking the reference poses to view poses mayfor example be performed at initialization of a service and/oriteratively at different time instants during the service. It will beappreciated that the receiver need not receive specific informationindicating a first-eye or second eye reference pose but that the imagesinherently correspond to such poses. The reference poses may bedetermined by setting them equal to a current view pose at a timeinstant and subsequent view poses may be determined relative to such anominal/reference view pose.

The first and second amounts may be absolute or relative amounts. Forexample, the first and second amounts may be first and second factorsfor scaling the difference between the first, and respectively second,depth values and the reference depth value.

The first-eye may be one of a left-eye and a right-eye of a viewer andthe second-eye may be the other of the left-eye and the right-eye of theviewer. In some embodiments, the first-eye may be the left-eye and thesecond-eye may be the right-eye, or vice versa. All references to thefirst-eye and the left-eye may in some examples be replaced byreferences to the left-eye and right eye respectively or may in someexamples be replaced by references to the right-eye and the left-eyerespectively.

In accordance with an optional feature of the invention, the depthprocessor is arranged to determine the reference depth value as apredetermined reference depth value.

This may allow low complexity, resource usage, and/or facilitateimplementation while providing high performance and an advantageous userexperience in many scenarios. The reference depth value may in someembodiments be a constant or fixed depth value and/or may be independentof any properties of the first or second depth values.

In accordance with an optional feature of the invention, the depthprocessor is arranged to determine a gaze point for a viewer in at leastone of the reference first-eye image and the reference second-eye image;and to determine the reference depth value in response to a depth valueof at least one of the first depth values and the second depth valuesfor the gaze point.

This may provide advantageous performance in many embodiments and mayspecifically reduce the perceptible impact of e.g. depth distortions inmany scenarios.

In accordance with an optional feature of the invention, the firstmodifier is arranged to reduce the difference between the first depthvalues and the reference depth value to substantially zero for at leastsome values of the difference between the first-eye view pose and thefirst-eye reference pose.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

The feature may specifically allow for a low complexity approach ofreducing in particular de-occlusion artefacts to be introduced forlarger differences between view pose and reference pose.

In some embodiments, the second modifier is arranged to reduce thedifference between the second depth values and the reference depth valueto substantially zero for at least some values of the difference betweenthe second-eye view pose and the second-eye reference pose

In accordance with an optional feature of the invention, the firstmodifier is arranged to not reduce the difference between the firstdepth values and the reference depth value for at least some values ofthe difference between the first-eye view pose and the first-eyereference pose.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

The feature may specifically allow a low complexity approach of reducingperceived depth/spatial distortions for smaller differences between viewpose and reference pose.

In some embodiments, the second modifier is arranged to not reduce thedifference between the second depth values and the reference depth valuefor at least some values of the difference between the second-eye viewpose and the second-eye reference pose.

In accordance with an optional feature of the invention, the firstmodifier is arranged to determine the first amount as a monotonicallyincreasing function of the difference between the first-eye view poseand the first-eye reference pose.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

This may provide an advantageous gradual trade-off between view shiftdegradation and depth adaptation distortion.

In some embodiments, the second modifier is arranged to determine thesecond amount as a monotonically increasing function of the differencebetween the second-eye view pose and the second-eye reference pose.

In accordance with an optional feature of the invention, the firstmodifier is arranged to generate modified depth values by scaling adifference between the first depth values and the reference depth valueby a scale factor having a value between zero and one for at least somevalues of the difference between the first-eye view pose and thefirst-eye reference pose.

In some embodiments, the second modifier is arranged to generatemodified depth values by scaling a difference between the second depthvalues and the reference depth value by a scale factor having a valuebetween zero and one for at least some values of the difference betweenthe second-eye view pose and the second-eye reference pose.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

In accordance with an optional feature of the invention, the scalefactor is a monotonically decreasing function of the difference betweenthe first-eye view pose and the first-eye reference pose for at least arange of the difference between the first-eye view pose and thefirst-eye reference pose.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

This may provide an advantageous gradual trade-off between view shiftdegradation and depth adaptation distortion.

In accordance with an optional feature of the invention, the scalefactor has a value between 0.95 and 1.05 for the difference between thefirst-eye view pose and the first-eye reference pose being below athreshold.

In many embodiments, the scale factor has a value of substantially onefor the difference between the first-eye view pose and the first-eyereference pose being below a threshold.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

The feature may specifically allow a low complexity approach of reducingperceived depth/spatial distortions for smaller differences between viewpose and reference pose.

In accordance with an optional feature of the invention, the synthesizeris arranged to shift the reference first-eye image and the referencesecond-eye image in the same direction.

In accordance with an optional feature of the invention, the firstmodifier is arranged to limit the difference between the first modifieddepth values and the reference depth value.

In some embodiments, the first modifier is arranged to limit thedifference between the first modified depth values and the referencedepth value to (be below) a limit.

This may provide a particularly advantageous user experience in manyembodiments. The corresponding feature may also be adopted by the secondmodifier.

The limit may be applied in only one direction and/or may be asymmetricand different in the forwards and backwards direction.

In many embodiments, the first modifier may be arranged to limit thedifference between the first modified depth values and the referencedepth value such that the first modified depth values are limited to beno further forward from the reference depth value than a limit.

In many embodiments, the first modifier may be arranged to limit thedifference between the first modified depth values and the referencedepth value such that the first modified depth values are limited to beno further backwards from the reference depth value than a limit.

In many embodiments, the first modifier may be arranged to limit anabsolute value of the difference between the first modified depth valuesand the reference depth values to be below a limit.

In accordance with an optional feature of the invention, the firstmodifier is arranged to apply a same relationship between the firstamount and the difference between the first-eye view pose and thefirst-eye reference pose as the relationship applied by the secondmodifier between the second amount and the difference between thesecond-eye view pose and the second-eye reference pose.

This may provide advantageous operation in many embodiments.

According to an aspect of the invention there is provided a method ofimage generation, the method comprising: determining a first-eye viewpose and a second-eye view pose; receiving a reference first-eye imagewith associated first depth values and a reference second-eye image withassociated second depth values, the reference first-eye image being fora first-eye reference pose and the reference second-eye image being fora second-eye reference pose; determining a reference depth value;generating modified first depth values by reducing a difference betweenthe first depth values and the reference depth value by a first amountdependent on a difference between the first-eye view pose and thefirst-eye reference pose; generating modified second depth values byreducing a difference between the second depth values and the referencedepth value by a second amount dependent on a difference between thesecond-eye view pose and the second-eye reference pose; and synthesizingan output first-eye image for the first-eye view pose by view shiftingthe reference first-eye image based on the modified first depth valuesand an output second-eye image for the second-eye view pose by viewshifting the reference second-eye image based on the modified seconddepth values.

These and other aspects, features and advantages of the invention willbe apparent from and elucidated with reference to the embodiment(s)described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the drawings, in which

FIG. 1 illustrates an example of elements of an image processing systemin accordance with some embodiments of the invention;

FIG. 2 illustrates an example of view poses;

FIG. 3 illustrates an example of elements of an image generatingapparatus in accordance with some embodiments of the invention;

FIG. 4 illustrates an example of depth variations and view poses;

FIG. 5 illustrates an example of a relationship between a differencebetween a view pose and a reference pose, and a scale factor;

FIG. 6 illustrates an example of depth variations and view poses;

FIG. 7 illustrates an example of a relationship between image positionsand position and depth perception for image objects;

FIG. 8 illustrates an example of a relationship between image positionsand position and depth perception for image objects;

FIG. 9 illustrates an example of a relationship between image positionsand position and depth perception for image objects;

FIG. 10 illustrates an example of a relationship between image positionsand position and depth perception for image objects;

FIG. 11 illustrates an example of depth variations and view poses.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates an example of a system that may embody examples andvariants of embodiments of the inventive concept.

In the example, a client in the form of an image generating apparatus101 is arranged to locally synthesize images based on images receivedfrom an image source apparatus 103. In the example, the images may beprovided in an image data stream transmitted (or possibly broadcast)from the image source apparatus 103 which operates as a remote server.The image source apparatus 103 is arranged to provide the image datastream via a network 105 which may for example be the Internet. Thearrangement may correspond to a client server arrangement andaccordingly the image generating apparatus 101 can also be referred toas the client and the image source apparatus 103 can also be referred toas the server.

As an example, the approach may be used to provide a remote conferenceservice or application, and the image source apparatus 103 may forexample operate as a conference bridge providing a video stream to theimage generating apparatus 101 which may operate as a conference client.It will be appreciated that the image generating apparatus 101 may insome embodiments also be arranged to capture local video and transmitthis to the image source apparatus 103 operating as a conference bridge.It will also be appreciated that the image data stream is in manyapplications, such as in a conference application, provided with anassociated audio stream thus providing a full audiovisualrepresentation.

It will also be appreciated that the described approach is not relianton a client server configuration but may be used in any configuration.For example, in some embodiments, two identical conference apparatusesmay directly communicate to enable a conference service. In such anexample, each apparatus may comprise functionality as described in thefollowing for both the image generating apparatus 101 and for the imagesource apparatus 103.

The image source apparatus 103 provides an image data stream whichcomprises images of the scene captured from different poses. Inparticular, it includes at least a first-eye (camera) imagecorresponding to a first-eye pose and a second-eye (camera) imagecorresponding to a second-eye pose. The image data stream mayspecifically provide a stereo image comprising the first-eye image andsecond-eye image or a moving sequence of stereo images (stereo video).

The references to first-eye and the second-eye will in the followingexamples and figures mainly refer to the left-eye and right-eye of aviewer respectively, but it will be appreciated that this may not be thecase in all examples. For example, in other examples, the references tofirst-eye and the second-eye may refer to the right-eye and left-eye ofa viewer respectively

In the field, the terms placement or a pose is used as a common term forposition and/or direction/orientation and the combination of theposition and direction/orientation of e.g. an object, a camera, or aview is indeed typically referred to as a pose or placement. Thus, aplacement or pose indication may comprise six values/components/degreesof freedom with each value/component typically describing an individualproperty of the position/location or the orientation/direction of thecorresponding object. Of course, in many situations, a placement or posemay be considered or represented with fewer components, for example ifone or more components is considered fixed or irrelevant (e.g. if allobjects are considered to be at the same height and have a horizontalorientation, four components may provide a full representation of thepose of an object). In the following the term pose is used to refer to aposition and/or orientation which may be represented by one to sixvalues (corresponding to the maximum possible degrees of freedom). Thedescription will focus on embodiments and examples where a pose has themaximum degrees of freedom, i.e. three degrees of freedom of each of theposition and the orientation resulting in a total of six degrees offreedom (6DoF). The pose may thus be represented by a set or vector ofsix values representing the six degrees of freedom and thus the posevector may provide a three-dimensional position and/or athree-dimensional direction indication. However, it will be appreciatedthat in other embodiments, the pose may be represented by fewer values.

It will be appreciated that in some embodiments, more than twosimultaneous images may be provided. For example, images may be providedfrom a linear array of cameras and the first-eye image and second-eyeimage may be selected as images from two of these cameras (with theselection typically being performed by the image generating apparatus101 based on the position of a viewer.

In addition to the first-eye image and the second-eye image, the imagedata stream comprises a set of depth values for the first-eye image,henceforth referred to as first depth values, and a set of depth valuesfor the second-eye image, henceforth referred to as second depth values.The depth values may be any suitable values and in any suitable form.Specifically, the depth values may be in the form of a first-eye depthmap and a second-eye depth map for the first-eye image and second-eyeimage respectively. The depth maps may directly comprise distance (inthe z-direction, i.e. perpendicular to the image plane) or disparityvalues.

The poses for which the first-eye image and second-eye image areprovided, i.e. the received first-eye pose and second-eye pose arereference poses for which the received first-eye image and second-eyeimage directly provide a stereo view for the scene.

In many embodiments, the image data stream may comprise only thereference first-eye image and the reference second-eye image with nospecific indication of specific associated reference poses except thatthey correspond to views of the same scene for respectively the firsteye and the second eye of a viewer, e.g. the left and right eyes of a(nominal) viewer. The image generating apparatus 101 may accordinglylink the images with locally determined reference poses which can beused as the basis for determining changes in the view poses. Forexample, at the start of a service the current pose of a viewer may beconsidered a nominal pose for which the received images are presenteddirectly, i.e. the nominal locally determined view poses for the firstand second eyes are considered to correspond to the poses of thereceived reference images. Thus, the first-eye reference pose isdetermined as the nominal first-eye view pose and the second-eyereference pose is determined as the nominal second-eye view pose, e.g,the first-eye reference pose is determined as the nominal left-eye viewpose and the second-eye reference pose is determined as the nominalright-eye view pose. Movements of the user from this nominal poseaccordingly results in dynamically changing view poses that aredetermined relative to the nominal/reference poses.

For view poses that correspond directly to the reference poses, theimage generating apparatus 101 may directly generate output imagescorresponding to the received first-eye image and second-eye image(which may accordingly also be referred to as reference images) and whenpresented to the left and right eyes of a user (e.g. by a dedicatedheadset or a stereo display (e.g. requiring the user to wear glasses))they may directly provide a 3D view of the scene.

However, if the user moves his head, the viewpoint and view pose willchange and for a natural experience it is desired that the imagespresented to the user changes to reflect this change. This may beachieved by performing a view point shift corresponding to the change inview poses from the reference view poses using the associated depthdata. However, the quality of such synthesized images may deterioratesubstantially unless the change in poses is very small. Therefore, theview point shift is in many scenarios preferably limited to a relativelysmall sweet spot.

For example, when multiple cameras are used to capture a 3Drepresentation of a scene, playback on a virtual reality headset isoften spatially limited to virtual viewpoints that lie close to theoriginal camera locations. This ensures that the render quality of thevirtual viewpoints does not show artefacts, typically the result ofmissing information (occluded data) or 3D estimation errors. Inside theso-called sweet spot, rendering can be done directly from one ormultiple reference camera images with associated depth map or mesh usingstandard texture mapping in combination with view blending.

This may be illustrated by the example of FIG. 2. In the example, eyepositions/poses are illustrated by triangles. In the example, afirst-eye view pose 201 (in the example being a left-eye view pose) anda second-eye view pose 203 (in the example being a right-eye view pose)are located with a distance of 2 cm to a reference first-eye pose 205(in the example being a reference left-eye pose) and a referencesecond-eye pose 207 (in the example being a left-eye view pose).Accordingly, images may be generated for the view poses 201, 203 by viewshifting of the received images for the reference poses 205, 207. In theexample, it is considered that the current view poses 201, 203 are atthe edge of a sweet spot for which the image quality of the images isconsidered acceptable. Accordingly, a problem will arise if the viewermoves any further away as image quality reduction and artefacts maybecome unacceptable.

Different solutions may be envisaged for such an issue. One approach maybe to switch the reference poses to coincide with the current viewposes, i.e. switch from providing view shifted images to providing thereceived reference images for the current view poses. Thus, effectively,for poses immediately outside the sweet spot, the view poses and thereference poses are realigned and movements around the new referencepose are then followed by view shifting relative to the new referencepose. However, such an approach will result in a sudden jump in theperceived view pose for the user (a significant parallax shift) whichtends to be perceived has highly unnatural and unpleasant experience.

Other solutions may include presenting blurred or darkened (or black)images when the view poses move outside the sweet spot. However, thisalso tends to provide an unnatural experience and limits the movementfreedom to typically a very small region.

FIG. 3 illustrates an example of an image generating apparatus 101 whichmay provide an improved user experience in many embodiments andscenarios, and which may in many scenarios provide an improved solutionto the above described issue (as well as typically other advantages andbenefits).

The image generating apparatus 101 comprises a receiver 301 whichreceives the image data stream from the image source apparatus 103.Thus, the receiver 301 receives at least a first-eye image with firstdepth values and a second-eye image with second depth values.Accordingly, image and depth are provided for at least a referencefirst-eye pose and a reference second-eye pose. In the following, itwill for brevity and clarity be considered that the depth values aredistance values provided in a depth map for each of the images.

The following will describe examples in which a first-eye image and asecond-eye image are received which are considered to have been directlycaptured e.g. by two cameras with an appropriate distance between them.However, it will be appreciated that the first-eye image and second-eyeimage can be generated in any suitable way, and e.g. that a highernumber of images for different poses can be received and the first-eyeimage and second-eye image can be selected or indeed generated fromthese.

For example, the approach can be used for a capture rig with manycameras. Camera selection logic can then be added such that an eye imageis synthesized from a nearby subset of reference camera images. Thesweet spot may then be defined as a distance function from the multiplereference camera positions.

The receiver 301 is coupled to a synthesizer 303 which is arranged togenerate output images for viewer poses. Accordingly, the imagesynthesizer 303 is fed the first-eye image and the second-eye image inorder to generate an output first-eye image and an output second-eyeimage, and specifically output left and right-eye images may begenerated.

The synthesizer 303 is coupled to a pose determiner 305 which isarranged to determine a first-eye view pose and a second-eye view pose.The first-eye view pose is a pose corresponding to the pose of anintended viewers first eye (e.g. left) and the second-eye view pose is apose corresponding to the intended viewers second eye (e.g. right).Thus, the first-eye view pose and the second-eye view pose correspond tothe poses for which view images are to be rendered by the imagegenerating apparatus 101 to provide a 3D image perception correspondingto the current pose of the viewer.

In some embodiments, the second-eye view pose and first-eye view posemay be determined individually and separately, e.g. based on individualmeasurements tracking the individual eye poses. However, in manyembodiments, the first-eye view pose and the second-eye view pose may bedetermined together and represented by common data combined with e.g.predetermined information of the relative pose differences between theeyes of a viewer. For example, a single viewer position, and possiblyhead rotation, may be determined and be indicative of the first-eye viewpose and the second-eye view pose. For example, it may be assumed thatthe eyes of a user have a predetermined distance (e.g. 6.3 cm in theexample of FIG. 2) and the first-eye view pose and second-eye view poseare thus uniquely known from a head position indicating the position ofan eye and a head rotation indicating the orientation of the head.Accordingly, in some embodiments, a single view pose may be estimated,and the first-eye view pose and second-eye view pose may be determinedand given by this view pose. Therefore, for simplicity, the descriptionmay also refer to a single view pose as representing the first-eye viewpose and the second-eye view pose, but it will be appreciated that sucha reference to a single view pose includes a reference to separatefirst-eye and second-eye view poses.

A view pose input may be determined in different ways in differentapplications. In many embodiments, the physical movement of a user maybe tracked directly. For example, a camera surveying a user area maydetect and track the user's head (or even eyes). In many embodiments,the user may wear a VR headset which can be tracked by external and/orinternal means. For example, the headset may comprise accelerometers andgyroscopes providing information on the movement and rotation of theheadset and thus the head. In some examples, the VR headset may transmitsignals or comprise (e.g. visual) identifiers that enable an externalsensor to determine the position of the VR headset.

In some systems, the rendering view pose may be provided by manualmeans, e.g. by the user manually controlling a joystick or similarmanual input. For example, the user may manually move the virtual vieweraround in the virtual scene by controlling a first joystick with onehand and manually controlling the direction in which the virtual vieweris looking by manually moving a second joystick with the other hand.

In some applications a combination of manual and automated approachesmay be used to generate the rendering view pose. For example, a headsetmay track the orientation of the head and the movement/position of theviewer in the scene may be controlled by the user using a joystick.

The pose determiner 305 is coupled to the image synthesizer 303 which isfed the first-eye view pose and the second-eye view pose. The imagesynthesizer 303 is arranged to synthesize an output first-eye image forthe first-eye pose from the reference first-eye image. Specifically,based on appropriate depth data, the image synthesizer 303 may perform aview shift operation to modify the reference first-eye image tocorrespond to a view image for the current first-eye pose. Such viewshifting is performed based on appropriate depth data and includeshorizontal shifting of image objects based on their depth as will beknown to the skilled person.

Similarly, the image synthesizer 303 is arranged to synthesize an outputsecond-eye image for the second-eye pose from the reference second-eyeimage. Specifically, based on appropriate depth data, the imagesynthesizer 303 may perform a view shift operation to modify thereference second-eye image to correspond to a view image for the currentsecond-eye pose.

It will be appreciated that the skilled person will be aware of manydifferent approaches and algorithms for such view shifting/synthesis andthat any suitable approach may be used. It will also be appreciated thatwhereas in many embodiments, the output first-eye image is generatedonly from the reference first-eye image and the output second-eye imageis generated only from the reference second-eye image, other images mayin some embodiments also be considered. For example, for a single eye,the output image could be generated by combining/using/blending multiplereference images.

The generation of the output first-eye image and the output second-eyeimage may thus be separate processes. The output first-eye image isgenerated from the reference first-eye image based on the correspondingfirst-eye poses and depth values whereas the output second-eye image isgenerated from the reference second-eye image based on the correspondingsecond-eye poses and depth values. Thus, the reference first-eye imageis shifted to provide the output first-eye image and the referencesecond image is shifted to provide the output second-eye image.

The view shift may in some cases be the same for both the first-eyeimage and the second-eye image, and thus the difference between theoutput first-eye pose and the reference first-eye pose may be the sameas the difference between the output second-eye pose and the referencesecond-eye image (such as e.g. in the example of FIG. 2). However, ingeneral, the pose differences may be different, e.g. a rotation of thehead around a point close to the first eye will result in no or littleposition change for the first-eye image but a significant change in theposition for the second-eye image. The individual generation of theoutput first-eye image and second-eye image may allow such differencesto easily be reflected in the generated output images.

Any difference measure indicative of the difference between two posesmay be used. For example, a difference measure determined as a distance(e.g. Euclidian and/or angular) between the two poses may be used. Inmost embodiments, the difference measure may be a scalar valueindicative of a magnitude or absolute value of the difference (such ase.g. a simple distance measure).

The difference between the view pose and the reference pose for thefirst and/or second eye may be determined in accordance with anysuitable distance or difference measure. The difference may for examplebe determined as a monotonically increasing function of the distancebetween a position of the view pose and a position of the reference poseand/or a monotonically increasing function of an (absolute value of an)angular difference between an orientation of the view pose and anorientation of the reference pose.

For example, in some embodiments, the difference between the view poseand the reference pose may be a difference between a view position and areference position. In such a case, any spatial distance measure may beused. For example, a Euclidian distance may be determined, or a distancealong a specific axis/direction may be used (e.g. only the distance inthe x-direction or z-direction may be used).

In some embodiments, the difference between the view pose and thereference pose may be a difference between a view orientation and areference orientation. In such a case, any angular difference ordistance measure may e.g. be used. For example, each of the orientationsmay be represented by a direction in the form of a vector, and thedifference measure may be determined as the (absolute value of the)angle between the two vectors in the plane comprising the two vectors(or as a monotonic function of these).

In some embodiments, the difference between the view pose and referencepose may reflect a difference between both a view orientation and areference orientation and between a view position and a referenceposition. For example, the distance measures mentioned in the previousparagraphs may be intermediate difference measures that are combined togenerate the final distance measure, e.g. by a weighted summation withthe weights set appropriately between the angular and position distancedifference measures. The weights may for example reflect the expectedrelative perceptual importance of each of the measures (and consider theunits for the values to provide a suitable conversion). In someembodiments, more complex combination functions may of course be used.For example, the weights of the weighted combination may themselves bedependent on the angular difference and the position distance measure.

As another example, in some embodiments where the view poses andreference poses are given by vectors comprising a number of positionand/or orientation coordinates, the difference may e.g. be determinedas:

$D = {\sum\limits_{i = 0}^{n}\;{\alpha_{i}{f_{i}\left( {p_{i,v} - p_{i,r}} \right)}}}$

where n is the number of coordinates in the vectors minus one, p_(i,v)is coordinate i of the view pose vector, p_(i,r) is coordinate i of thereference pose vector, ƒ_(i)(p_(i,v)−p_(i,r)) is a monotonic function ofthe absolute value of p_(i,v)-p_(i,r), and α_(i) is a weight factor forcoordinate i. In such an embodiment, the difference measure can e.g. bereduced to a position distance measure by setting the weight factor tozero for all orientation coordinates, and the difference measure cane.g. be reduced to an orientation difference by setting the weightfactor to zero for all position coordinates.

Thus, the image synthesizer 303 generates an output stereo image whichcorresponds to the current view pose. As long as the difference betweenthe reference and the output/synthesis view poses is sufficiently small(within the sweet spot) this can be done with high image quality andtypically without it being perceptible to the viewer that images aresynthesized by view shifting. Accordingly, in a dynamic, real timeapplication, the output stereo images may accordingly be dynamicallyupdated to follow small head movements of the user. For example, correctstereopsis and motion parallax may be provided for a user nodding orshaking his head etc.

However, the apparatus of FIG. 3 further comprises means for adaptingthe operation based on the difference between the reference pose and theview pose. Specifically, rather than use the received depth valuesdirectly when synthesizing the images, the apparatus may adapt/modifythe depth values depending on the difference between the reference andsynthesis/output view poses.

Specifically, the apparatus comprises a first modifier 307 which isarranged to generate modified first depth values from the received firstdepth values, and a second modifier 309 which is arranged to generatemodified second depth values from the received second depth values. Themodified depth values are fed to the image synthesizer 303 where theyare used for the synthesis of respectively the output first-eye imageand the output second-eye image.

The modification is based on a reference depth value and accordingly theapparatus further comprises a depth processor 311 which is arranged todetermine a reference depth value and feed it to the first and secondmodifiers 307, 309.

The first modifier 307 is arranged to generate the modified first depthvalues by reducing a difference between the received reference firstdepth values and the reference depth value by an amount that depends ona difference between the first-eye view pose and the first-eye referencepose. Similarly, the second modifier 309 is arranged to generatemodified second depth values by reducing a difference between thereceived reference second depth values and the reference depth value byan amount that depends on a difference between the second-eye view poseand the second-eye reference pose. The amount of the reduction may insome scenarios be the same but will typically not be identical (andindeed the difference between the view poses and the reference poseswill typically be different).

In the apparatus, the depth values that are used for synthesis may thusbe modified such that the difference to a reference depth value isreduced by an amount which depends on the difference between the viewpose and the reference pose for that eye. The amount of the reductionmay typically be a monotonic function of the (absolute value) of thedifference (e.g. distance). The depth values for a given image may thusbe brought closer to a reference depth value the larger the differencebetween view pose and the reference pose for the eye.

However, the reduction is applied individually to the depth values forthe first-eye image and the second-eye image. Thus, the reduction indepth with respect to the reference depth value for one of the imagesmay reduce the amount of view shift that is applied to the individualimage. However, the disparities between the different eye images is notremoved and therefore the 3D perception of depth remains.

As a low complexity example, the reference depth value may be set to apredetermined depth value. For example, for a conference application itmay be assumed that the typical distance from a stereo camera to theperson being captured is, say, 1.2 m. Accordingly, the reference depthvalue may be set to the depth value corresponding to this distance, i.e.corresponding to 1.2 m.

The first modifier 307 and the second modifier 309 may typically applythe same function to determine the amount of reduction to apply suchthat the same difference between view pose and reference pose results inthe same reduction (whether in absolute or relative terms). As a lowcomplexity example, it may be considered that for poses within the sweetsport, no reduction is applied and for poses outside the sweet spot, alldepth values are set equal to the reference depth value. Thus, if thefirst-eye view pose is within the sweet spot of the reference first-eyepose (say the distance is less than 2 cm), then no change is applied tothe first depth values. However, if it is outside the sweet spot, thenall depth values are set constant to the reference depth value, e.g. toa depth value corresponding to a distance of 1.2 m.

Accordingly, when performing view shift to the reference first-eyeimage, a first-eye view pose within the sweet spot will result in a fullview pose shift resulting in an image being generated corresponding tothe new pose. However, if the first-eye view pose is outside the sweetspot, then the view shift may be based on the same depth value for allpixels and image objects. This will simply result in the output imagebeing generated to correspond to the reference input image but with allpixels shifted in the same direction and by the same amount.

The same approach is independently performed for the second-eye image.

Thus, for increasing distance to the reference pose, the depth variationis reduced for each of the first-eye image and second-eye imagesindividually. This results in less differentiation in the shifting ofobjects in the image thereby reducing the image quality degradation andartefact introduction (e.g. there is less de-occlusion).

However, the depth reduction does not result in an output stereo imagebeing generated which lacks depth, i.e. it does not result in a 2Dstereo image being generated. Rather, the generated output image for thefirst and second eye images may each have less depth variation withinthem in terms of individual variations within the image, but the depthdifference represented by the disparities between the received referencefirst-eye image and second-eye image is maintained.

Indeed, it has been found in practice that whereas the approach mayintroduce some distortion when the distance between view poses andreferences poses increase too much, the overall effect is perceived ashighly advantageous. Indeed, the effect is described as a naturalperception and gradual degradation. It has been found that asatisfactory 3D user experience can be perceived for larger posevariations. In particular, it has been found that the approach mayprovided improved perceived consistency between motion parallax andstereopsis cues for poses outside the sweet spot.

It should be noted that the image synthesizer 303 shifts the referencefirst-eye image and the reference second-eye image in the same directionfor the same direction of the difference between the reference pose andview pose. Thus, often a head movement results in the first-eye viewpose and second-eye view pose moving in the same direction, and theresulting shifts applied by the image synthesizer 303 may accordingly bein the same direction. Thus, the effective view pose changesaccordingly. This is in contrast e.g. to situations where the disparityoffset between first and second eye images are adapted to change thedepth that corresponds to the display/image plane (i.e. moving thingsforward or back relative to the screen). In such cases, disparity ischanged by moving corresponding pixels/image objects in oppositedirections.

In many embodiments, the amount of reduction with respect to a referencedepth level changes gradually with respect to the difference between theview pose and the reference pose for at least some values of thedifference. Thus, for at least some values of the difference, the amountof reduction may be a one to one function of the difference and viceversa, i.e. it may have one to one correspondence and be a bijectivefunction. Thus, for a range of values for the difference, there may be aone to one mapping to a corresponding range of the amount of reduction.The one to one mapping may specifically be a monotonically increasingone to one mapping to a range of the amount. Thus, an increasingdifference results in an increasing amount of reduction (and thus adecreasing difference between the modified value and the reference depthvalue). The one to one mapping may specifically be to a range of theamount from no reduction (i.e. no change in the depth value) to a 100%reduction (setting the modified depth value equal to the reference depthvalue).

In many embodiments, the reduction in the difference between thereceived depth value and the reference depth value may be achieved byscaling the difference between the depth value and the reference depthvalue by a positive value less than one. Thus, the first modifier 307may be arranged to generate modified depth values by scaling adifference between the first depth values and the reference depth valueby a scale factor having a value between zero and one for at least somevalues of the difference between the first-eye view pose and thefirst-eye reference pose. Similarly, the second modifier 309 may bearranged to generate modified depth values by scaling a differencebetween the second depth values and the reference depth value by a scalefactor having a value between zero and one for at least some values ofthe difference between the view second-eye pose and the second-eyereference pose.

The scaling may typically be the same for both the first modifier 307and the second modifier 309, i.e. they may be identical and apply thesame scaling for the same difference.

An example of the approach is shown in FIG. 4. In the example, areference depth value is indicated by the depth line 3 whereas the inputdepth is indicated by depth line 1. As illustrated by the example, whenthe view poses are such that they coincide with the reference poses(situation 1) then the output depth values may be generated to beidentical to the input depth values, i.e. a scale factor of 1 isapplied. When the view poses are very far from the reference poses(situation 3), the modified depth values may all be set to be identicalto the reference depth value, i.e. a scale factor of zero is applied tothe difference between the received depth value and the reference depthvalue. For a view pose in between (situation 2 in the example, justoutside the sweet sport), a scaling value between 0 and 1 may be appliedthereby biasing the depth values towards the reference depth value.

In many embodiments, the difference between the reference depth valueand the reduced depth values may be reduced to substantially zero, i.e.the modified depth values may be set substantially identical to thereference depth value, for at least some values of the difference.Specifically, if the (magnitude/absolute value) of the differencebetween the view pose and reference pose exceeds a threshold, themodified depth values may be set identical to the reference depth value.This may for example be achieved by setting the scale factor to zero forthese values. As a result, the modified depth values will all beconstant, and the view shift performed by the image synthesizer 303 willresult in all pixels being shifted by the same amount.

In many embodiments, the first modifier 307 and the second modifier 309may be arranged to not modify the depth values for at least some valuesof the difference between the corresponding view pose and referencepose. Specifically, the first modifier 307 may be arranged to not reducethe difference between the first depth values and the reference depthvalue for at least some values of the difference between the first-eyeview pose and the first-eye reference pose. Similarly, the secondmodifier 309 may be arranged to not reduce the difference between thesecond depth values and the reference depth value for at least somevalues of the difference between the second-eye view pose and thesecond-eye reference pose. Specifically, the modifiers 307, 309 maygenerate the modified depth values to be identical to the received depthvalues if (the magnitude/absolute value of) the difference is less thana threshold. The threshold may be selected to correspond to the regionfor which it is considered that the resulting image quality from viewshifting is sufficient (e.g. with no degradation being perceptible),i.e. it may be selected to correspond to the sweet spot.

This may specifically be achieved by setting the scale factor equal toone for the difference between the view pose and reference pose meetinga criterion, such as the difference being below a thresholdcorresponding to the sweet spot.

In the following a specific example will be provided in which such anapproach is used to modify depth values. In the example, d_(eye) is usedto denote the difference between the view pose and the reference posewhich in the specific example is determined as the Euclidean distancebetween the current eye (first or second) 3D position and the referencecamera view position for the camera that is used for synthesis of a newview for this eye. We now introduce a radius parameter R₁ for thespherical sweet spot. A typical value for R₁=0.01 m when renderingcaptured scenes with objects as close-by as 0.25 m. We also introduce asecond radius parameter R₂ with a typical value of R₂=0.1 which is thedistance beyond which we will have scaled the depth map back to a plane(no remaining depth variation).

Let z_(ref) denote the assumed reference plane towards which we wishscale the depth map, i.e. it represents the reference depth value.Please note that the reference depth may be a constantly changing valuethat correspond with the observed depth in the gaze direction of theviewer. For each pixel (i,j) in the depth map (i.e. for each depth valuein the depth map), we now calculate the difference with the referencedepth:

Δ(i,j)=z(i,j)−z _(ref).

We also calculate the scale factor that we apply depending on thedistance of the eye to the center of the sweet spot:

$s = \left\{ {\begin{matrix}1 & {{{if}\mspace{14mu} d_{eye}} < R_{1}} \\{1 - {\min\left( {\frac{d_{eye}}{R_{2}},1} \right)}} & {{{if}\mspace{14mu} d_{eye}} \geq R_{1}}\end{matrix}.} \right.$

The scale factor s reduces to 0 when d_(eye)=R₂. FIG. 5 shows the scalefactor as a function of the difference d_(eye).

The depth is now modified as:

z _(out)(i,j)=z _(ref) +sΔ(i,j).

In the example, the same relationship between the amount of reduction(the scale factor) and the differences in pose is used for both thefirst-eye image and the second-eye image, i.e. the above description maybe considered to apply individually to both the first modifier 307 andthe second modifier 309.

It will be appreciated that whereas the specific example uses a scalefactor to reduce the difference between depth values and the referencedepth value, other approaches may be used in other embodiments. Forexample, a variable depth offset may be subtracted from the receiveddepth values with this offset being dependent on the difference betweenthe view pose and reference pose.

In the previous example, the reference depth value was determined as apredetermined, fixed value that is selected depending on the specificsetup. For instance 0.75 m for a typical conferencing distance of 0.75 mor 1.5 m for a typical conferencing distance of 1.5 m. However, in manyembodiments, the reference depth value may be a dynamically determinedvalue.

For example, in many embodiments, the depth processor 311 may bearranged to determine the reference depth value in response to the firstand/or second depth values for the reference images. For example, thereference depth value may be determined as the average depth value orthe depth value of an image object. For example, face detection may beused to detect an image object corresponding to a face and the referencedepth value may be set to the average depth value for the identifiedimage object.

In many embodiments, the depth processor 311 may be arranged todetermine the reference depth value based on a gaze of the viewer.

The depth processor 311 may specifically comprise a gaze estimator whichis arranged to estimate a gaze point in the first-eye image and/or inthe second-eye image. The gaze point is indicative of the viewers gazewithin the image, and thus reflects where in the image the user islooking.

The gaze point may for example be determined by capturing camera imagesof the observer and extracting the eye image regions after facedetection. The pupil can then be detected since this is a relativelydark region. The position of the pupil relative to the eye region can beused to calculate the gaze direction in 3D space. This can be done usingcameras that are integrated in a display or using cameras that areintegrated into a virtual reality headset. An even simpler approach isto assume that the gaze direction corresponds with the viewer direction(head orientation). The gaze point can then be assumed to correspondwith the center point for each first/second eye image.

The reference depth value may then be set to a depth value for the gazepoint. For example, if the gaze point is considered to define a specificpixel, the reference depth value may be set to the depth value of thatpixel. If the gaze point is considered to have a spatial extension, thereference depth value may e.g. be set to the average of the depth valueswithin an area corresponding to the gaze point. The reference depthvalue may in some embodiments be determined based on the first-eye imageand in other embodiments based on the second-eye image, or may indeed bebased on both. For example, a gaze point may be determined in both thefirst-eye image and the second-eye image and the reference depth valuemay be set as the average of the corresponding depth values in the twoimages. This may in many embodiments provide a substantially improveduser experience and may substantially reduce the perceptibility of anydistortion resulting from the modifications of depth values for largerdistances to the reference pose.

The approach specifically reflects the realization that the perceivedeffect of spatial distortions heavily depend on where in the scene theviewer is looking. For instance, when the viewer happens to be lookingat a distant object, he does not observe parallax changes due to viewpose shifting. The most important parts of an image are concentrated ina small solid angle around the gaze direction/point. Therefore, reducingparallax distortions and changes in the gaze direction may substantiallyimprove the perceived image quality.

FIG. 6 illustrates the situation corresponding to FIG. 5 but with theviewer changing his gaze point to the most forward part of the scene. Asa result, the reference depth value changes to the most forward depth,and the scaling that dependents on the pose difference is now relativeto this depth, i.e. relative to the most forward part of the scene. Theexample may thus reflect the application of a scale factor around thedepth that corresponds to a person's gaze direction (typically theobject of attention). As a result, the perceived parallax change reducesin the gaze direction when a person moves outside the sweet spot.

It should be noted that a particularly advantageous effect is that theperceived 3D experience and depth of the scene is not removed even forlarger differences between the view pose and the reference pose. Thus,whereas the depth variation for the individual image is reduced therebyreducing artefacts and degradation by the individual view shiftoperation (e.g. due to de-occlusion), the disparity between the outputfirst-eye image and second-eye image is maintained thereby keeping astereoscopic 3D effect when presented to the two eyes of a viewer.

Simplistically, it can be exemplified by a consideration that whereasthe effect on each individual image is to reduce the depth towards a“flat” image, the two images together still provide a stereo image withdisparity between the left and right image (between the first and secondimages, or vice versa) and thus provide a perception of depth in thescene. The output first-eye image and output second-eye imageaccordingly include stereopsis clues.

This may be illustrated by considering a specific example.

FIG. 7 shows a scenario in which a traditional stereoscopic display maypresent a stereo image on a suitable display panel 701 at a givendistance from a viewer. In this case, two image points i₁ ^(L) and i₁^(R), corresponding to one point on an object, are presented torespectively the left and right eyes of a viewer. A user with eyes atpositions (p_(L), p_(R)) will perceive the point/object to be at a depthposition p_(i). In this example, there is no depth data provided withthe stereo images and accordingly no view shifting is performed, and theimage points do not change position. As a result, if the viewer moveshis eyes from positions (p_(L), p_(R)) to positions(p_({tilde over (L)}), p_({tilde over (R)})), the virtual 3D objectpoint also moves from position p_(i) to position {tilde over (p)}₁.Accordingly, a change in position including a change of the depth of theobject occurs when the user changes viewpoint. However, for a correctmotion parallax, the object point should remain stationary when theviewer moves his head. The stereoscopic and motion parallax cues are notconsistent in such a traditional approach.

FIG. 8 illustrates a corresponding example but where depth data isavailable and suitable view shifting is performed based on the changesin viewer pose. In this example, when the viewer moves his head, theimage points are moved accordingly on the display panel (curved arrows).As a result, the object point p₁ remains stationary when the viewermoves his head and the stereoscopic and motion parallax cues areconsistent. However, for larger shifts, the view shift may introduceerrors, degradations, or artefacts.

FIG. 9 illustrates the example of FIG. 8 but further considering asecond object point p₂ which is at a different depth z₂. When the viewermoves the head, depth data is again used to perform view shifting.However, the size of the required shift depends on the depth of thepoint and since the second point lies at a larger depth, its motionparallax (curved arrows) for each eye will be smaller than for the firstpoint. The stereoscopic and motion parallax cues remain consistent forboth object points but degradation due to view shifting occurs forlarger view shifts.

FIG. 10 illustrates the approach of the described apparatus where thedepth variations have been reduced for each individual image. As aconsequence of the reduced depth variation around the reference depthvalue, the difference in the variation in the applied view shift forpoints at different depths in the scene is reduced and specifically ifthe depth is set to be the same for all values (i.e. the modified depthvalues are set equal to the reference depth value) then the shifts willbe identical. A substantial advance of this is that it may reducedegradation in image quality resulting from the view shift. Inparticular, it may reduce or indeed remove de-occlusion as all pixelsare moved in the same direction and possibly by the same amount.

However, as illustrated in FIG. 10, the second object point p₂ will beshifted by a wrong amount for the depth z₂. This will result in theshifted object point being perceived to be at a different position{tilde over (p)}₂. including at a different depth {tilde over (z)}₂. Thestereoscopic and motion parallax cues are accordingly consistent for thefirst point but not for the second point.

However, the perceived scene is still a three dimensional scene andindeed the perceived position shift may often be relatively small.Further, in the described approach the trade-off between the imagequality degradation and the position consistency can flexibly be adapteddependent on the difference between the view pose and the referencepose.

In addition, if the reference depth value is adapted based on the gazepoint, the perceptible impact of distortions to objects at other depthsmay be reduced substantially and indeed typically if the viewer has agaze in the direction of the first point in the example, he may not evennotice the inconsistency regarding the second point.

In many embodiments, the first modifier 307 may be arranged to apply alimit to the difference between the generated first modified depthvalues and the reference depth value. Similarly, the second modifier 309may be arranged to apply a limit to the difference between the generatedsecond modified depth values and the reference depth value. Thus, thedepth values may be constrained with respect to the reference depthvalue by the application of a maximum and/or minimum depth value. Insome embodiments, a limit may be applied only in one direction (e.g. amaximum forward or backwards value may be defined) but in otherembodiments limits may be applied both for increasing and decreasingdepth values.

An example of a scenario with depth limits is illustrated in FIG. 11. Inthe example, clipping of the depth values to values between z_(far) andz_(near) is applied in order to further reduce view shift artefacts.

In the specific example, objects close to the viewer are displayed withtheir true depth induced motion parallax since the near clipping planelies closer to the viewer than the closest object. However, the depth ofobjects that lie just a little distance behind the reference plane willbe clipped at the far clipping plane z_(far). As a result, not muchdepth variation will be allowed behind the reference plane which willreduce rendering errors and de-occlusion artefacts.

As the reference depth can change continuously depending on the dynamicviewing-direction or gaze direction of the observer, so can the near andfar clipping planes. For instance, we can force the depth variation inthe resulting view to always have a maximum distortion (warp distance)of 10 pixels and select the near and far depth clipping range such thatthis maximum warp distance is kept. In practice this could mean that thenear and far clipping ranges lie close to the reference depth when thisreference depth lies close to the observer (nearby objects give largerparallax) and conversely they lie further away from the reference depthwhen this depth is larger. In this way, image rendering quality can becontrolled independent of the reference depth. In some embodiments, theclipping planes can also be introduced in a gradual manner (as thescaling), e.g. the further the deviation from the sweet spot, the closereach clipping plane moves to its final fixed value.

The terms first and second may be replaced by left and right,respectively or vice versa. E.g. the terms first-eye view pose,second-eye view pose, reference first-eye image, and referencesecond-eye image may be replaced by left-eye view pose, right-eye viewpose, reference left-eye image, and reference right-eye image,respectively (or vice versa).

It will be appreciated that the described approaches and principles canbe applied in many different and varied applications and scenarios, andthat the previous description for clarity has focused on a less complexexample.

For example, the approach could be used for playback of the widely used360 omnidirectional stereo (ODS) format. Indeed, it would be possible touse the described principles even without transmission of dense depthmaps. For example, an ODS player could include graphics card shader codethat could perform a single disparity measurement on a small image patch(e.g. a region of 32×32 pixels) in the center of the stereo eye-pairthat is already being extracted from the ODS format during rendering(i.e. essentially at the very end of the rendering pipeline). Thissingle depth value can then be applied to all pixels using anothershader (global shift on both images). When looking around in 360, themotion parallax effect will be adopted to the overall depth in a certaindirection (e.g. a person standing close versus everything being far awayin another direction).

The invention can be implemented in any suitable form includinghardware, software, firmware or any combination of these. The inventionmay optionally be implemented at least partly as computer softwarerunning on one or more data processors and/or digital signal processors.The elements and components of an embodiment of the invention may bephysically, functionally and logically implemented in any suitable way.Indeed, the functionality may be implemented in a single unit, in aplurality of units or as part of other functional units. As such, theinvention may be implemented in a single unit or may be physically andfunctionally distributed between different units, circuits andprocessors.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term comprising does not exclude the presence ofother elements or steps.

Furthermore, although individually listed, a plurality of means,elements, circuits or method steps may be implemented by e.g. a singlecircuit, unit or processor. Additionally, although individual featuresmay be included in different claims, these may possibly beadvantageously combined, and the inclusion in different claims does notimply that a combination of features is not feasible and/oradvantageous. Also the inclusion of a feature in one category of claimsdoes not imply a limitation to this category but rather indicates thatthe feature is equally applicable to other claim categories asappropriate. Furthermore, the order of features in the claims do notimply any specific order in which the features must be worked and inparticular the order of individual steps in a method claim does notimply that the steps must be performed in this order. Rather, the stepsmay be performed in any suitable order. In addition, singular referencesdo not exclude a plurality. Thus, references to “a”, “an”, “first”,“second” etc. do not preclude a plurality. Reference signs in the claimsare provided merely as a clarifying example and shall not be construedas limiting the scope of the claims in any way.

1. An image generating apparatus comprising: a determiner circuit,wherein the determiner circuit is arranged to determine a first-eye viewpose and a second-eye view pose; a receiver circuit, wherein thereceiver circuit is arranged to receive a reference first-eye image withassociated first depth values and a reference second-eye image withassociated second depth values, wherein the reference first-eye image isfor a first-eye reference pose and the reference second-eye image is fora second-eye reference pose; a depth processor circuit, wherein thedepth processor circuit is arranged to determine a reference depthvalue; a first modifier circuit, wherein the first modifier circuit isarranged to generate modified first depth values by reducing adifference between the first depth values and the reference depth valueby a first amount, wherein the modified first depth values are dependenton a difference between the first-eye view pose and the first-eyereference pose; a second modifier circuit, wherein the second modifiercircuit is arranged to generate modified second depth values by reducinga difference between the second depth values and the reference depthvalue by a second amount, wherein the modified second depth values aredependent on a difference between the second-eye view pose and thesecond-eye reference pose; and a synthesizer circuit, wherein thesynthesizer circuit is arranged to synthesize an output first-eye imagefor the first-eye view pose by view shifting the reference first-eyeimage based on the modified first depth values, wherein the synthesizercircuit is arranged to synthesize an output second-eye image for thesecond-eye view pose by view shifting the reference second-eye imagebased on the modified second depth values.
 2. The image apparatus ofclaim 1, wherein the depth processor circuit is arranged to determinethe reference depth value as a predetermined reference depth value. 3.The image apparatus of claim 1, wherein the depth processor circuit isarranged to determine a gaze point for a viewer in at least one of thereference first-eye image and the reference second-eye image, whereinthe depth processor circuit is arranged to determine the reference depthvalue in response to a depth value of at least one of the first depthvalues and the second depth values for the gaze point.
 4. The imageapparatus of claim 1, wherein the first modifier circuit is arranged toreduce a difference between the first depth values and the referencedepth value to substantially zero for at least some values of adifference between the first-eye view pose and the first-eye referencepose.
 5. The image apparatus of claim 1, wherein the first modifiercircuit is arranged to not reduce a difference between the first depthvalues and the reference depth value for at least some values of thedifference between the first-eye view pose and the first-eye referencepose.
 6. The image apparatus of claim 1, wherein the first modifiercircuit is arranged to determine the first amount as a monotonicallyincreasing function of a difference between the first-eye view pose andthe first-eye reference pose.
 7. The image apparatus of claim 1, whereinthe first modifier circuit is arranged to generate modified depth valuesby scaling a difference between the first depth values and the referencedepth value by a scale factor, wherein the scale factor has a valuebetween zero and one for at least some values of a difference betweenthe first-eye view pose and the first-eye reference pose.
 8. The imageapparatus of claim 7, wherein the scale factor is a monotonicallydecreasing function of a difference between the first-eye view pose andthe first-eye reference pose for at least a range of the differencebetween the first-eye view pose and the first-eye reference pose.
 9. Theimage apparatus of claim 7, wherein the scale factor has a value between0.95 and 1.05.
 10. The image apparatus of claim 1, wherein thesynthesizer circuit is arranged to shift the reference first-eye imageand the reference second-eye image in the same direction.
 11. The imageapparatus of claim 1, wherein the first modifier circuit is arranged tolimit the difference between the first modified depth values and thereference depth value.
 12. The image apparatus of claim 1, wherein thefirst modifier circuit is arranged to apply a same relationship betweenthe first amount and the difference between the first-eye view pose andthe first-eye reference pose as the relationship applied by the secondmodifier circuit between the second amount and the difference betweenthe second-eye view pose and the second-eye reference pose.
 13. A methodof image generation, the method comprising: determining a first-eye viewpose and a second-eye view pose; receiving a reference first-eye imagewith associated first depth values and a reference second-eye image withassociated second depth values, wherein the reference first-eye image isfor a first-eye reference pose, wherein the reference second-eye imageis for a second-eye reference pose; determining a reference depth value;generating modified first depth values by reducing a difference betweenthe first depth values and the reference depth value by a first amount,wherein the modified first depth values is dependent on a differencebetween the first-eye view pose and the first-eye reference pose;generating modified second depth values by reducing a difference betweenthe second depth values and the reference depth value by a secondamount, wherein the modified second depth values is dependent on adifference between the second-eye view pose and the second-eye referencepose; and synthesizing an output first-eye image for the first-eye viewpose by view shifting the reference first-eye image based on themodified first depth values and an output second-eye image for thesecond-eye view pose by view shifting the reference second-eye imagebased on the modified second depth values.
 14. A computer program storedon a non-transitory medium, wherein the computer program when executedon a processor performs the method as claimed in claim
 19. 15. Themethod of claim 12, wherein the reference depth value is a predeterminedreference depth value.
 16. The method of claim 12, further comprising:determining a gaze point for a viewer in at least one of the referencefirst-eye image and the reference second-eye image; and determining thereference depth value in response to a depth value of at least one ofthe first depth values and the second depth values for the gaze point.17. The method of claim 12, further comprising reducing a differencebetween the first depth values and the reference depth value tosubstantially zero for at least some values of a difference between thefirst-eye view pose and the first-eye reference pose.
 18. The method ofclaim 12, further comprising not reducing a difference between the firstdepth values and the reference depth value for at least some values ofthe difference between the first-eye view pose and the first-eyereference pose.
 19. The method of claim 12, further comprisingdetermining the first amount as a monotonically increasing function of adifference between the first-eye view pose and the first-eye referencepose.
 20. The method of claim 12, further comprising generating modifieddepth values by scaling a difference between the first depth values andthe reference depth value by a scale factor, wherein the scale factorhas a value between zero and one for at least some values of adifference between the first-eye view pose and the first-eye referencepose.